The present invention relates generally to refrigeration systems. More particularly, the invention is directed to an evaporatively-cooled, direct-expansion refrigeration system that can be constructed at a reduced cost in relation to conventional refrigeration systems of similar capability. The invention is also directed to a method of operating such a system.
FIG. 1 depicts an evaporatively-cooled, direct-expansion refrigeration system 10 of conventional design. The refrigeration system 10 comprises a compressor 12, a condenser 14, an evaporative subcooler 16, an expansion device 18, and an evaporator 20. The compressor 12, condenser 14, evaporative subcooler 16, expansion device 18, and evaporator 20 are interconnected by piping 22.
A refrigerant, e.g., halocarbon, enters the compressor 12 as superheated vapor (see arrow 26 in FIG. 1). The compressor 12 raises the pressure and temperature of the superheated refrigerant. The high-pressure, superheated refrigerant is circulated to the condenser 14 by way of the piping 22 (arrow 28). The refrigerant is cooled and condensed to saturated liquid in the condenser 14. In particular, thermal energy is transferred from the refrigerant to the ambient environment in the condenser 14.
The refrigerant is drawn out of the condenser 14 by gravity, and is subsequently routed through the evaporative subcooler 16 (arrow 30). The refrigerant is subcooled in the evaporative subcooler 16, i.e., the temperature of the refrigerant is reduced below the refrigerant""s saturation temperature (as in the condenser 12, thermal energy is transferred from the refrigerant to the ambient environment in the evaporative subcooler 16). Subcooling is necessary to prevent vaporization of the refrigerant due to pipe friction after the refrigerant leaves the evaporative subcooler 16. Subcooling also increases the effectiveness of the evaporator 20, thereby improving the overall efficiency of the refrigeration system 10.
The subcooled refrigerant subsequently flows to the expansion device 18 (arrow 32). The pressure and the temperature of the refrigerant are reduced as the refrigerant passes through the expansion device 18. The lower-pressure, lower-temperature refrigerant then flows to the evaporator 20 via the piping 22 (arrow 34). The heat-transfer medium that is to be chilled or cooled, e.g., water, is circulated into and out of the evaporator 20 via piping 25 (arrows 36 and 38). The subcooled refrigerant absorbs thermal energy from the heat-transfer medium, thereby chilling or cooling the medium and providing the desired refrigerating effect. The refrigerant is typically superheated to approximately ten degrees Fahrenheit in the evaporator 20. Superheating is necessary to ensure that potentially damaging liquid droplets are not present in the refrigerant when the refrigerant reenters the compressor 12 upon leaving the evaporator 20. The above-noted cycle is started once again upon the return of the superheated refrigerant to the compressor 12.
The use of the evaporative subcooler 16 in the conventional refrigeration system 10 presents substantial disadvantages. For example, the coils of a typical evaporative subcooler such as the subcooler 16 are relatively large, thereby increasing the refrigerant-charge requirements for the system 10. Also, the cost of an evaporative subcooler typically represents a substantial portion of the initial overall cost of a refrigeration system such as the system 10. Furthermore, evaporative subcoolers are usually heavy, and occupy a relatively large volume of equipment space. These characteristics are particularly disadvantageous in rooftop installations, where constraints are commonly imposed on the allowable dimensions and weight of the evaporative subcooler.
In light of the above discussion, it is evident that an unfilled need exists for an evaporatively-cooled, direct-expansion refrigeration system that operates without the use of an evaporative subcooler.
An object of the present invention is to provide an evaporatively-cooled, direct-expansion refrigeration system that operates without the use of an evaporative subcooler. In accordance with this objective, a presently-preferred refrigeration system comprises a compressor for increasing a temperature and a pressure of a refrigerant, and a condenser fluidly coupled to an outlet of the compressor for condensing the refrigerant. The presently-preferred system also comprises an expansion device for decreasing the temperature and pressure of the refrigerant, and an evaporator fluidly coupled to an outlet of the expansion device for evaporating the refrigerant by transferring thermal energy between the refrigerant and a second fluid. The presently-preferred system further comprises a heat exchanger having a first flow path fluidly coupled to an inlet of the compressor and an outlet of the evaporator, and a second flow path fluidly coupled to an outlet of the condenser and an inlet of the expansion valve. The heat exchanger is adapted to superheat the refrigerant in the first flow path and subcool the refrigerant in the second flow path by transferring thermal energy between the refrigerant in the first and second flow paths.
A further object of the present invention is to provide a method for lowering a temperature of a heat-transfer medium. In accordance with this object, a presently-preferred method of lowering a temperature of a heat-transfer medium comprises compressing a superheated refrigerant to increase a temperature and a pressure thereof, condensing the compressed refrigerant, and subcooling the condensed refrigerant. The presently-preferred method further comprises expanding the subcooled refrigerant to decrease the temperature and pressure thereof, and evaporating the expanded refrigerant by transferring thermal energy to the expanded refrigerant from the heat-transfer medium. The presently-preferred method also comprises superheating the evaporated refrigerant by transferring thermal energy to the evaporated refrigerant from the condensed refrigerant.
A further object of the present invention is to provide a method for operating an evaporatively-cooled, direct-expansion refrigeration system without the use of an evaporative subcooler. In accordance with this object, a presently-preferred method of operating a refrigeration system comprises flowing a superheated refrigerant through a compressor to raise a temperature and a pressure of the superheated refrigerant, flowing the compressed refrigerant through a condenser to condense the compressed refrigerant, and flowing the condensed refrigerant through a first flow path of a heat exchanger to subcool the condensed refrigerant. The presently-preferred method also comprises flowing the subcooled refrigerant through an expansion device to lower the temperature and pressure of the refrigerant, and flowing the expanded refrigerant through an evaporator to evaporate the expanded refrigerant and transfer thermal energy to the expanded refrigerant from a second fluid. The presently-preferred method further comprises flowing the evaporated refrigerant through a second flow path of the heat exchanger to superheat the evaporated refrigerant by transferring thermal energy from the condensed refrigerant to the evaporated refrigerant.